Retrofit of structural steel columns using FRP-concrete composite systems

Fiber reinforced polymer (FRP)-confined concrete-steel composite columns have been investigated as a retrofit technique for structural steel columns. However, the application techniques required to utilize this type of composite column in a retrofit scenario have not yet been fully developed. This paper investigates the use of a split tube that can be placed around an existing steel column to act as stay in place formwork. The split tubes used in this study are manufactured from glass fiber reinforced polymer (GFRP) sheets. The split tube elements surrounding the steel column are then wrapped with carbon fiber reinforced polymer (CFRP) sheets. The void between the steel section and the FRP tube is subsequently filled with concrete to create a composite column. The uniaxial CFRP sheets are applied in the hoop direction to provide confinement to the concrete. An experimental investigation has been completed to evaluate the relative performance of this composite system. A total of twelve stub columns, consisting of four different column types have been tested. Experimental findings demonstrate the improved performance of the proposed retrofit technique.